It works for the h:mm field but not the AM/PM drop down when a field rule is applied to the time field.

When field rule is 'show always':

the field's AM/PM drop down is read-only:

When the form is used NOT as a preview, but in an instance, the time field shows as read-only:

So, this whole bug seems like it is a big deal when in preview, but when in actual use it behaves as expected.

^this was misleading. The form loads correctly as read-only, but if you use field rules to show or hide the time field, it reverts back to the bug (h:mm stays read-only but AM/PM dropdown is editable). This just confirm the issue lies with the field rules. 

A few points of clarification:

• this appears in both preview and instance of the form
• if I create a new form and test this, the time field is completely read-only
• the form this issue is occurring on was created before Update 3, then the time field was added after Update 3
• this is a time ONLY field and not a Date/Time field
• this can be reproduced on command in separate forms instances

kudos to @████████ for spotting the relationship to Field Rules!

I'll now try and do that with jQuery, but wanted to report it for fix.

jQuery fix:

//set time fields to RO 
$('.departTime select, .returnTime select').attr('readonly', true).change();